1. Field of the Invention
The present invention relates generally to apparatuses for use in polymerase chain reaction (hereinafter referred to as “PCR”) and more particularly, to an apparatus for holding a test tube for insulated isothermal PCR.
2. Description of the Related Art
In the filed of biotechnology, polymerase chain reaction (PCR) is a well-known technology used to amplify specific nucleic acid sequences. The PCR process comprises three major steps including denaturation, primer annealing and extension, which require different reaction temperatures. The required temperature for the denaturation step is typically in a range between 90° C. and 97° C. The required temperature for the primer annealing step will depend on the melting temperature of the primer used. Typically, the annealing temperature ranges from 35° C. to 65° C. The required temperature for the extension step is typically about 72° C.
The insulated isothermal PCR is based on Rayleigh-Bénard convection, which is driven by buoyancy when heating fluid layer from below, is a common physical phenomenon. The insulated isothermal PCR is generally performed by immersing the bottom of a test tube which contains a reaction mixture into a hot water in such a way that the rest portion of the test tube is exposed to atmosphere at room temperature for heat dissipation. As a result, the temperature of the reaction mixture will gradually decrease from the bottom of the reaction mixture having a temperature of about 97° C. toward the liquid level of the reaction mixture having a temperature of about 35° C. Because of the temperature gradient, the heat convection is induced, such that the reaction mixture will flow through various regions having different temperatures and then undergo different reaction steps.
In the conventional apparatus for performing a convection PCR, because the portion of the test tube, which is exposed to the ambient air at room temperature for heat dissipation, has a low heat dissipating rate, the temperature at the liquid level of the reaction mixture will become higher and higher due to the increment of the heating time. As a result, the temperature at the liquid level of the reaction mixture may rise to a degree higher than the required temperature suitable for conducting the primer annealing step before the convection PCR has been performed completely. Under this circumstance, the polymerase chain reaction may break, such that a desired, large amount of copies of specific nucleic acid sequences may not be obtained.